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virus: Rethinking Sex
« on: 2004-08-23 23:45:54 » |
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Rethinking Sex
Robert Dorit
Evolution's Rainbow: Diversity, Gender, and Sexuality in Nature and People.
Joan Roughgarden. viii + 474 pp. University of California Press, 2004.
$27.50.
More than 2,400 years ago, Socrates was charged with using philosophy to
"study things in the sky and beneath the earth"—with seeking a material
understanding of the world, in effect, rather than accepting
well–established theistic narratives. He defended himself in an
Apologia—a passionate and intellectually rigorous speech that made clear
the grounds for his opinions and actions. As recorded by Plato, it
stands as one of the defining documents of Western culture.
Evolution's Rainbow is Joan Roughgarden's Apologia, an extraordinary
book that entwines a radical attack on the Darwinian concept of sexual
selection with a personal narrative written from her perspective as a
transgendered woman (until six years ago, she was Jonathan Roughgarden).
The book is thought–provoking, even at times profound, although some of
its arguments are infuriatingly extraneous or superficial. Some critics
will dismiss it as a book with an agenda—polemic tainted by the author's
unwillingness to detach her scientific analyses from her personal
experience. To take that narrow view, however, does grave injustice to
Roughgarden's ambitious undertaking.
The book's scope is broad and inclusive. Part I, titled "Animal
Rainbows," surveys the natural history of two thorny subjects: sex and
gender. Consider, for instance, the fact that sexual reproduction is
itself a fundamental evolutionary paradox. Parthenogenetic
reproduction—cloning—produces offspring that are virtually genetically
identical to their mother. In contrast, making offspring with a partner
may seem like a good idea for a variety of reasons, but those offspring
will share only half of a given parent's genes. Sex thus comes at a
cost. Although a number of competing theories for the evolution of
sexual reproduction have been put forth, we still have no unanimously
accepted explanation.
The matter only gets more complicated when we consider the myriad ways
in which evolution has seen fit to embody the sexes, in apparent
disregard of our binary expectations. Despite the determination of many
of us to partition the living world into neat, discrete categories of
male and female, the living world does not comply. Sex is itself a fuzzy
term: Is sex determined by the chromosomal makeup of cells, so that any
mammal with a Y chromosome is male? Should sexual distinctions be made
with regard to the set of developmental events that result in
recognizably male and female characteristics (genitalia and secondary
sexual traits)? Or should definitions be based on behavior—that is,
should some unambiguous set of displays be considered the mark of
maleness or femaleness?
Roughgarden's expertise as an evolutionary ecologist is apparent in her
fascinating accounts of species in which no simple binary division of
sex applies. Nearly half of the females in certain species of South
American hummingbirds, for instance, are characterized by male
coloration, and on occasion a small percentage of the males sport female
colors. Roughgarden also has the reader consider the aptly named hamlets
(small bass that live around coral reefs), which are simultaneously male
and female, and can switch between producing sperm and producing eggs in
the span of a single mating episode. To be or what to be, indeed.
What are we to make of the many examples of hermaphroditism and sex–role
reversal, of intersexed deer and pouched male kangaroos? One choice,
which Roughgarden soundly rejects, is to consider these phenomena
oddities—or worse, pathologies. As she indicates, the central
philosophical legacy of the Darwinian revolution supplies an alternative
perspective. Diversity of sexual forms, in a post–Darwinian world, is
not simply noise, nor is it the flawed expression of some underlying
Platonic dichotomy. Instead, diversity is the message itself—the very
stuff of evolution, the rainbow alluded to in the title of the book.
Roughgarden urges a broad and liberating definition of sex and gender.
Sex, she argues, boils down to the size of the haploid gametes produced:
Males produce small gametes, females produce large ones. Gender, she
suggests, is "the appearance, behavior and life history of a sexed
body." In this formulation, the many reproductive strategies,
appearances, behaviors and social systems cease to be departures from
the norm and become instead examples of the rich tapestry of adaptation
in nature.
Roughgarden, however, has more in mind than making a plea for a more
expansive perspective on sex and gender in the natural world.
Ambitiously, she pronounces dead the theory of sexual selection, an
important beam in the Darwinian edifice. In its stead, she sketches a
theory of social selection that makes possible a more expansive and
diversity–valuing vision of sex and gender. All of this before the
reader is midway through the book.
Roughgarden's objections to Darwinian sexual selection deserve careful
analysis. Sexual selection, which Darwin first proposed in On the Origin
of Species in 1859 and elaborated on to a much greater extent in The
Descent of Man in 1871, accounts for features of organisms that appear
to have little or no functional significance and that sometimes even
appear to hinder survival: the preposterous feathers of the peacock, the
predator–attracting call of the bullfrog and the overdecorated nests
built by male bowerbirds, to name a few.
Darwin ably argued that the evolution of such traits was driven not by
their effect on survival but instead by their contribution to
reproductive success. When females choose males that exhibit
ever–more–elaborate versions of a particular trait, they set in motion a
process that can result in extraordinarily baroque structures in one sex
(usually, but not always, males) and is virtually absent in the other
sex. The theory of sexual selection, like so much in Darwin, is framed
in the language of economics: Sperm are cheap, whereas eggs are
expensive. Females invest more in reproduction, which forces them to be
more selective, whereas males diversify their reproductive investment.
Roughgarden, claiming that "sexual selection theory has now been
discredited," proposes a different, more globalized economic model of
social selection, in which competition among males for access to females
is replaced by cooperation, both within and between sexes. In this
model, females are no longer seen as the sole resource limiting
reproduction. Instead, we are urged to consider all the resources—food,
nesting sites, parental care and partners—that are necessary to ensure
successful reproduction. Any strategies that increase an individual's
access to and control of such resources—including, under certain
ecological circumstances, same–sex mating, sex–role reversals and
multigendered societies—will be favored.
Roughgarden argues that binary sexes thus become a special case in which
males are simply a "special adaptation for the home delivery of sperm";
the ancestral condition is one in which male and female functions
coexist in a single body. Similarly, Roughgarden's model suggests that
most of the elaborate sex–specific traits we marvel at are not the
result of male competition for female attention but rather are
social–inclusionary traits—membership signals guaranteed access to
valuable resources (think "secret handshake"). Elaborate feather
displays and decorated bowers are not simply billets–doux from one sex
to the other but are instead subtle social signals to all members of the
group.
It is much too early to tell whether Roughgarden's theory of social
selection will prove to be a productive revision of evolutionary theory
or will simply contribute to a broadening of existing models of sexual
and kin selection. I don't anticipate that the prevailing theory of
sexual selection will simply ride off quietly into the sunset: Many of
its predictions have been borne out over the past 150 years. Yet the
rise and fall of theories in science is not simply an objective matter
of weighing the evidence. The success of social selection theory may
well depend on its ability to subsume the theory of sexual selection.
But regardless of the eventual success of the formulation, Evolution's
Rainbow will change the way many biologists view the world, making it
easier for them to see additional instances of diversity in genders,
sexual phenotypes and sex roles. More important, Roughgarden provides a
theoretical framework into which such observations can be placed,
turning anomalies into useful data. That's real progress.
The second section, "Human Rainbows," reviews the biology of sex
determination and the diversity of gender expression in humans,
emphasizing how our 30,000 or so genes interact with one another and
with the cellular, physiological and ecological environment in which
development takes place. Human diversity thus derives both from the
genetic uniqueness of individuals and from the number of developmental
interactions involved in transforming a fertilized zygote into a
reproductive adult. The sheer quantity and complexity of those
interactions virtually guarantee that no two trajectories—and thus no
two outcomes—will be alike.
This interactionist perspective contributes much to our understanding of
sex determination and sex differences. We live in an age wedded both to
the primacy of genes as causes of biological phenomena and to the notion
that sex is binarily and irreversibly determined at the moment of
conception. We imagine sex to be determined by tightly linked causes and
effects that lead, for example, from the presence of a Y chromosome to
the development of a male body and then to a set of behaviors, all in
the service of reproduction. This book reminds the reader that these
connections are flexible and modifiable. Seen in this light, sex
differences look like almost all data in biology: Males and females
vary, and male and female distributions for the vast majority of traits
overlap.
In a chapter titled "Gender Identity," Roughgarden brings observations
about natural history and developmental biology to bear on an
exploration of human gender identity and sexual orientation. I confess I
always feel some trepidation when evolutionary biologists take on human
behavior. Hapless academics often find themselves caught between the
Scylla of anthropomorphizing animal behavior and the Charybdis of
reducing human culture and behavior to a set of fitness–enhancing
traits. Roughgarden is no exception. When I read about "lesbian
lizards," I flinch, because the expression suggests that an evolutionary
explanation that accounts for female–female courtship in lizards will
have something useful to say about human lesbianism. It won't unless
lizard same–sex courtship and human same–sex courtship have the same
evolutionary origins (that is, they are homologous behaviors) or unless
same–sex courtship evolved in lizards and in humans in response to
similar ecological pressures (making them convergent behaviors). I worry
that human and lizard behaviors may be neither homologous nor convergent
but may simply share some superficial similarities. Human behavior,
driven by our greatest evolutionary innovation, the 20–billion–neuron
neocortex, has made the search for homology far more complicated.
But my most serious disagreement with Roughgarden concerns her attempts
to find an adaptive explanation for the varieties of human sexuality and
gender orientation she so ably describes. To make of all human
behavioral diversity an adaptation risks returning the analysis of sex
and gender to the very reductive and speculative quagmire from whence
she has just extracted it.
I applaud her use of a Darwinian framework to de–pathologize difference.
Exploding the notion that all sexual and gender diversity results from
conditions or syndromes that require a cure is an undertaking both
scientifically sound and long overdue. Individuals who cannot easily be
classified as either male or female continue to be squeezed by reductive
biological explanations (a gene that causes homosexuality, a cluster of
neurons that is larger or smaller in transgendered individuals, and so
forth), ill–defined or overly rigid medical and psychiatric
classifications (penis length at birth of less than 1.5 centimeters
makes an intersexed baby "female") and political forces that rabidly
cling to a cultural construct of what supposedly is or is not "natural."
This book will help readers question their assumptions and examine their
prejudices in the bright light of reason.
Perhaps everything we do has an effect on our survival and reproduction,
but that does not make every behavior an adaptation, evolved to ensure
future representation. Roughgarden's apparent insistence on viewing all
human behavior as adaptation forces her into an unconvincing
quantitative argument. She suggests that gay, lesbian and transsexual
individuals together amount to about 5 percent of the U. S. population—a
frequency that is, she says, too high for those gender expressions to be
considered "genetic defects," because traits that reduce fitness by even
a mild 5 percent become increasingly rare, eventually stabilizing at a
frequency of around 1 in
50,000 (0.002 percent).
Leaving aside the many demographic and chromosomal circumstances under
which selection cannot purge genetic defects, this argument abandons the
rigor and subtlety in the classification of sex and gender that the book
pleads for, implying that gender orientation can be thought of as an
obvious trait with a simple underlying basis. The frequency of gay,
lesbian and transgender people does not require an adaptive explanation,
and seeking one pulls Roughgarden into needless and untestable speculation.
The final section of the book, "Cultural Rainbows," presents comparative
anthropological perspectives on sex and gender. This material is a
tantalizing, if superficial, reminder of how greatly human constructions
of gender and sexuality vary across cultures. By introducing the
vestidas (transgender sex workers) of Mexico City and the hijras of
India (a castelike group of more than one million transgender people),
Roughgarden reminds us that we have a choice: We can accept the
struggles and discourse of all people at face value, or we can try to
fit them into preexisting categories. More important, these examples
underscore the extent to which those categories are contingent products
of our own culture, and not something natural. Autres pays, autres
moeurs—every time and place defines and redefines sex, gender and
normalcy. Reread the Bible or the Koran or the legend of Joan of Arc
carefully, Roughgarden tells us, and you'll find a more nuanced
understanding of sexuality and gender than you perhaps expected.
I hope this book will be widely read. It combines the combustible power
of a keen intellect with powerful conviction and ethical courage.
Scientists are trained to create the illusion of objectivity by hiding
their hopes and expectations. Roughgarden tries a different approach,
openly injecting her reasoned convictions and policy agenda into her
analyses. I don't agree with all of her conclusions, but she has written
an important and honest book about a subject that matters. Reviewer
Information
Robert Dorit is an associate professor in the Department of Biological
Sciences at Smith College.
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